Anatomy of the very tiny: First description of the head skeleton of the rare South American catfish sarcoglanis simplex (Siluriformes: Trichomycteridae)

The osteology of Sarcoglanis simplex, a rare, miniature South American catfish, is described for the first time based on a single, 17 mm adult specimen that was both cleared and Alizarin-stained, and visualized with microfocus computed tomography (MicroCT). Previously, the internal skeletal features of this species could be predicted based only on conditions observed in its closest relatives within the subfamily Sarcoglanidinae of the Trichomycteridae. The relatively new MicroCT technique successfully revealed fine details of the skeletal morphology of this tiny fish. As predicted, Sarcoglanis shares with Staurogianis, Stenolicmus, Malacoglanis, Microcambeva, and Ammoglanis an anterior ossification of the palatine and a large posteriorly directed dorsal process on the quadrate. Contrary to predictions, however, the mesethmoid of Sarcoglanis does not have the distal ends of the comua distinctly wider than at their bases, and the anterior margin of the mesethmoid is not convex.